Authors
Schmid MR, Loughran SP, Regel SJ, Murbach M, Bratic Grunauer A, Rusterholz T, Bersagliere A, Kuster N, Achermann P. Sleep EEG alterations: effects of different pulse-modulated radio frequency electromagnetic fields. J Sleep Res. Apr 12, 2011. Ahead of print.
Introduction
Several studies have demonstrated that exposure to radiofrequency electromagnetic fields (RF-EMFs) leads to an increase in EEG spectral power during sleep. This increase has mainly been observed in the spindle frequency range (11-15 Hz) during non-rapid eye movement sleep, both during and after RF-EMF exposure. It has been shown that these changes in electrical brain activity are induced by pulse modulated but not by continuous wave RF EMFs. It is not clear which components of the RF EMF are responsible for the observed EEG changes. Studies of potential effects of RF-EMFs on cognitive performance produce inconsistent results.

Objective
The first objective of this study was to find out which field parameter is responsible for the observed changes in electrical brain activity during sleep. The hypothesis was that pulse modulation component in the sleep frequency range (~14 Hz) acts as a mediator of these effects. The second objective was “to address previous inconclusive results regarding the effects of exposure to pulse-modulated RF EMF on cognition”. Methods
The study was carried out in the sleep laboratory of the Institute of Pharmacology and Toxicology, University of Zurich. Participants were 30 healthy non-smoking men aged 20-26 years who were free of sleep problems. The participants were exposed at weekly intervals to three different conditions (a pulse-modulated RF EMF at 14 Hz, a pulse modulated RF EMF at 217 Hz and a sham exposure) for 30 min before going to bed. A peak spatial specific absorption rate for active conditions was 2 W/kg. The exposure conditions were applied in a randomized double-blind crossover design. During the exposures, the participants performed three cognitive tasks (simple reaction time task, 2-choice reaction time task and N-back task) to measure attention, reaction speed and working memory. After exposure, the subjects were asked to identify the exposure condition. Prior to bedtime and in the morning they completed questionnaires rating their moods and well-being. EEG was continuously recorded during the 8-hour sleep.

Results and Interpretation
There was no effect of any exposure condition on the subjects’ cognitive performance. Consistent with previous research, a significant increase in EEG spectral power was observed during non-rapid eye movement sleep following the 14-Hz pulse-modulated exposure condition. This finding suggests that the 14-Hz pulse modulation component, which is close to the physiological sleep spindle frequency, acts as a mediator of the changes in brain electrical activity. A smaller and non-significant increase in EEG spectral power was seen after the 217-Hz pulse-modulated exposure. The subjects could not correctly identify the exposures. There were no differences in subjective moods, well-being or sleep quality between the conditions.

Conclusion
The authors have concluded that, despite the observed short-term effects of pulse-modulated RF EMF on sleep EEG, there was no indication of an effect of RF exposure on cognition, objective or subjective sleep quality.